Casting member and method for manufacturing same

ABSTRACT

Disclosed are an inexpensive casting member on which a film with high peel strength is formed, and a method for manufacturing the casting member. A surface-treated mold ( 1 ) includes a metal mold ( 10 ) having the molding surface including a plurality of protrusions ( 11 ) each having an inverse-slope shape, and a carbon film ( 20 ) formed on the molding surface of the metal mold ( 10 ). The surface-treated mold ( 1 ) is manufactured through a step (S 1 ) including a modeling step (S 10 ) for producing the metal mold ( 10 ), by means of selective laser sintering, which has the molding surface including the plurality of protrusions ( 11 ) each having the inverse-slope shape, and a film-forming step (S 20 ) for forming the carbon film ( 20 ) on the molding surface of the metal mold ( 10 ) produced in the modeling step (S 10 ).

TECHNICAL FIELD

The present invention relates to a casting member such as a metal mold,and to a method for manufacturing the casting member.

BACKGROUND ART

Conventionally, widely known is a technique on a casting member such asa metal mold, by which a film such as a carbon film includingnanocarbons is formed on a part of the surface of the casting member(e.g. on the molding surface of the casting member) in order toaccomplish decrease of mold-release resistance and the like.

Moreover, publicly known is a technique for making a part, on which thefilm is to be formed, of the surface of a casting member bumpy by meansof shot blasting or the like to increase surface area of the part,thereby inhibiting the film from peeling from the part (for example, seePatent Literature 1).

However, if the surface of the casting member is worked by means of theshot blasting or the like, the surface area of the worked part is notsufficiently increased. Therefore, it is expected that peel strength ofthe film is further increased.

Moreover, the surface processing such as the shot blasting needs to beadditionally performed when the casting member as mentioned above ismanufactured, which causes problems that cost required for manufacturingthe casting member is increased for example.

CITATION LIST Patent Literature

Patent Literature 1: JP 2011-156549 A

SUMMARY OF INVENTION Problem to be Solved by the Invention

The objective of the present invention is to provide an inexpensivecasting member on which a film with high peel strength is formed, and amethod for manufacturing the casting member.

Means for Solving the Problem

A first aspect of the invention is a casting member used for casting,which includes a base material manufactured by means of selective lasersintering, which has a surface including a plurality of minuteirregularities each having an inverse-slope shape, and a film formed onthe surface of the base material.

Preferably, the base material is a metal mold having a molding surface,and the film is formed on the molding surface of the base material.

A second aspect of the invention is a method for manufacturing a castingmember used for casting, which includes a modeling step for producing abase material, by means of selective laser sintering, which has asurface including a plurality of minute irregularities each having aninverse-slope shape, and a film-forming step for forming a film on thesurface of the base material.

Preferably, the film is a carbon film including at least one kind ofnanocarbon, and in the film-forming step, the carbon film is formed onthe surface of the base material by heating the base material whilesupplying a reactive gas used to make the carbon film.

More preferably, a temperature and a time for heating the base materialin the film-forming step are set to a temperature and a time forperforming an aging treatment for hardening the base material,respectively.

EFFECTS OF THE INVENTION

The present invention makes it possible to inexpensively inhibit a filmfrom peeling off.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a surface-treated mold according to an embodiment of thepresent invention.

FIG. 2 shows a step for manufacturing the surface-treated mold.

FIG. 3 is a timing chart showing a film-forming step.

FIG. 4 is a timing chart showing an aging treatment of a conventionalmetal mold.

FIG. 5 is a timing chart showing a step for forming a carbon film on themolding surface of the conventional metal mold.

DESCRIPTION OF EMBODIMENTS

With reference to FIG. 1, described below is a surface-treated mold 1 asan embodiment of a casting member according to the present invention.

As shown in FIG. 1, the surface-treated mold 1 includes a metal mold 10as a base material, and a carbon film 20 formed on the molding surfaceof the metal mold 10.

The metal mold 10 is used for die casting or the like, and has a surface(upper surface in FIG. 1) formed as the molding surface. The metal mold10 is produced by means of selective laser sintering, the surfacethereof is rough owing to a plurality of minute irregularities.

The selective laser sintering is a technique for, while laminatinglayers consisting of predetermined metal powder (e.g. maraging steelpowder), melting a predetermined part of each of the layers with a laserso as to model a product with a desired shape. The selective lasersintering is known as a type of rapid prototyping.

Through the selective laser sintering, the metal powder melts andsolidifies. Therefore, the plurality of minute irregularities is formedon the surface of the metal mold 10, which makes the surface of themetal mold 10 rough.

The plurality of minute irregularities formed on the surface of themetal mold 10 produced by means of the selective laser sinteringconsists of a plurality of protrusions 11.

For convenience, described below is only the plurality of protrusions 11on the molding surface of the metal mold 10 which forms a part of thesurface of the metal mold 10.

The protrusion 11 protrudes from the molding surface of the metal mold10 toward the outside (upper side in FIG. 1), and has an inverse-slopeshape (what is called an undercut shape). Specifically, the protrusion11 is formed to gradually increase in width (dimension in the right-leftdirection in FIG. 1) from the base end (bottom end in FIG. 1) to theprotruding end (top end in FIG. 1) thereof. In other words, the distancebetween the adjoining protrusions 11 gradually decreases toward theoutside (upper side in FIG. 1) of the metal mold 10.

Thus, the molding surface of the metal mold 10 is formed as a bumpysurface consisting of the plurality of protrusions 11. In other words,the molding surface of the metal mold 10 includes the plurality ofminute irregularities each having the inverse-slope shape (what iscalled the undercut shape).

The carbon film 20 is a dense film for reducing mold-release resistanceof the molding surface of the metal mold 10, for preventing the moldingsurface of the metal mold 10 from melting, and the like. In the presentembodiment, the carbon film 20 includes at least one kind of nanocarbon.

In the present invention, the nanocarbon is a microscopic fibrousnanocarbon such as carbon nanofiber, carbon nanotube, carbon nanocoil,or carbon nanofilament.

For example, the carbon film 20 may consist of a plurality of carbonnanofibers formed on the molding surface of the metal mold 10, or mayconsist of a plurality of carbon nanotubes formed on the molding surfaceof the metal mold 10. In addition, substantially spherical fullereneseach consisting of a plurality of carbon atoms may be applied to thefibrous nanocarbons such as carbon nanofibers.

The carbon film 20 covers the plurality of protrusions 11 on the moldingsurface of the metal mold 10, and fills every space between theadjoining protrusions 11.

Thereby, anchor effect is produced between the carbon film 20 and theplurality of protrusions 11.

Specifically, the plurality of protrusions 11 upward protrudes from themolding surface of the metal mold 10, thereby restraining the carbonfilm 20 from moving in a direction (right-left direction in FIG. 1)parallel to the molding surface of the metal mold 10. In addition, sincethe protrusion 11 has the inverse-slope shape (what is called theundercut shape), the plurality of protrusions 11 restrains the carbonfilm 20 from moving in a direction (top-bottom direction in FIG. 1)perpendicular to the molding surface of the metal mold 10.

Therefore, the anchor effect produced between the carbon film 20 and theplurality of protrusions 11 inhibits the carbon film 20 from peelingfrom the molding surface of the metal mold 10.

As mentioned above, in the surface-treated mold 1, the molding surfaceof the metal mold 10 is formed as a bumpy surface consisting of theplurality of protrusions 11 each having the inverse-slope shape (what iscalled the undercut shape), and the carbon film 20 is formed on themolding surface of the metal mold 10.

This makes it possible to make the area of the molding surface of themetal mold 10 larger than that of the molding surface (e.g. moldingsurface worked by means of shot blasting) of a conventional metal mold,and to form more nanocarbons on the molding surface of the metal mold10.

Therefore, it is possible to strongly combine the carbon film 20 withthe molding surface of the metal mold 10, and to inhibit the carbon film20 from peeling from the molding surface of the metal mold 10.

Moreover, more nanocarbons are formed on the molding surface of themetal mold 10, thus enabling to form the carbon film 20 with largerthickness (vertical dimension in FIG. 1).

Therefore, it is possible to improve adiabaticity of the molding surfaceof the metal mold 10, and consequently to suitably flow molten metalthereon during casting. In addition, the carbon film 20 suitably holds arelease agent, thus enabling to improve oil-retentivity of the moldingsurface of the metal mold 10.

In the present embodiment, the carbon film 20 including at least onekind of nanocarbon is used as a film according to the present invention,but the film is not limited thereto.

For example, a dense film such as hard chromium plating, or black rustmay be used as the film according to the present invention.

With reference to FIGS. 2 to 5, described below is a step S1 formanufacturing the surface-treated mold 1 as an embodiment of a step formanufacturing a casting member according to the present invention.

As shown in FIG. 2, the step S1 includes a modeling step S10 and afilm-forming step S20.

The modeling step S10 is a step for producing, by means of the selectivelaser sintering, the metal mold 10 having the molding surface whichincludes the plurality of minute irregularities each having theinverse-slope shape (what is called the undercut shape).

In the modeling step S10, the metal mold 10 having the molding surfaceon which the plurality of protrusions 11 is formed is made from metalpowder such as maraging steel powder by means of the selective lasersintering.

The film-forming step S20 is a step for forming the carbon film 20 onthe molding surface of the metal mold 10.

In the film-forming step S20, the metal mold 10 is heated whilesupplying reactive gas used to make the carbon film 20, such asacetylene gas, to the metal mold 10 under an atmosphere of inert gassuch as nitrogen in an atmosphere furnace, thereby forming the carbonfilm 20 on the molding surface of the metal mold 10.

It is preferable that an aging treatment for hardening the metal mold 10is performed while forming the carbon film 20 on the molding surface ofthe metal mold 10 in the atmosphere furnace.

Specifically, as shown in FIG. 3, after changing an atmosphere in theatmosphere furnace into an atmosphere of nitrogen (N₂), the atmosphereis heated to 570° C. while supplying acetylene (C₂H₂) and ammonia (NH₃)to the inside of the atmosphere furnace. Then, the metal mold 10 isheated for 4 hours while maintaining the temperature.

Consequently, the carbon film 20 is formed on the molding surface of themetal mold 10, and the aging treatment is applied to the metal mold 10.

As shown in FIG. 4, in a conventional aging treatment, a metal mold isheated at 570° C. for 4 hours.

In the film-forming step S20 according to the present embodiment, themetal mold 10 is heated at the same temperature and for the same time asthe conventional aging treatment.

Therefore, through the film-forming step S20, the aging treatment isapplied to the metal mold 10.

As shown in FIG. 5, conventionally, a carbon film is formed on themolding surface of a metal mold at a temperature (480° C.) lower thanthat at which the aging treatment is performed. In other words, thetemperature at which the carbon film is formed on the molding surface ofthe metal mold is different from the temperature at which the agingtreatment is performed.

However, the carbon film formed on the molding surface of the metal molddoes not deteriorate by oxidation if the temperature of the carbon filmis not over 600° C. Therefore, the carbon film may be formed on themolding surface of the metal mold at the temperature (570° C.) at whichthe aging treatment is performed.

In the present embodiment, the metal mold 10 is heated at 570° C. in thefilm-forming step S20, but the temperature at which the metal mold 10 isheated is not limited thereto.

The temperature at which the carbon film 20 is formed on the moldingsurface of the metal mold 10 is preferably 400° C. (temperature at whichnanocarbons can form) or more, and the temperature at which the agingtreatment of the metal mold 10 is performed is preferably 350° C. ormore. Therefore, the temperature at which the metal mold 10 is heated inthe film-forming step S20 is preferably 400° C. or more.

Additionally, as mentioned previously, since the carbon film 20 maydeteriorate by oxidation at a temperature higher than 600° C., thetemperature at which the metal mold 10 is heated in the film-formingstep S20 is preferably 600° C. or less.

Therefore, it is preferable that the temperature at which the metal mold10 is heated in the film-forming step S20 is 400 through 600° C.

In the case of forming the carbon film on the molding surface of themetal mold at the same temperature and for the same time as the agingtreatment of the metal mold, if a quantity of reactive gas such asacetylene gas supplied to the metal mold is reduced by approximately 20%of a conventional quantity (quantity of the reactive gas supplied to themetal mold in the case of forming the carbon film at a temperature lowerthan that at which the aging treatment of the metal mold is performed),the quality of the carbon film hardly varies. Therefore, the quantity ofthe reactive gas such as acetylene gas supplied thereto may be changed(reduced) depending on conditions of the aging treatment of the metalmold. In the present embodiment, the time for supplying ammonia (NH₃) isreduced in order to make the supply of the ammonia (NH₃) smaller than aconventional supply thereof (see the hatched areas in FIGS. 3 and 5).Note that the supply of nitrogen (N₂) is increased instead of reducingthe supply of the ammonia (NH₃).

Moreover, depending on the conditions of the aging treatment of themetal mold, the time for heating the metal mold may be changed so thatthe quality of the carbon film hardly varies.

Thus, the temperature and the time for forming the carbon film 20 arechanged so that the quality of the carbon film 20 hardly varies, and areequalized to those for performing the aging treatment of the metal mold10. This makes it possible to concurrently performing, in thefilm-forming step S20, the formation of the carbon film 20 on themolding surface of the metal mold 10, and the aging treatment of themetal mold 10.

Therefore, it is possible to reduce the time and the cost required formanufacturing the surface-treated mold 1 without additionally performingthe aging treatment of the metal mold 10.

Generally, after the aging treatment of the metal mold is performed, astep for forming a carbon film on the molding surface of the metal mold.The metal mold hardened through the aging treatment is heated again whenthe carbon film is formed on the molding surface of the metal mold, andthereby the effect of the aging treatment is weakened. However, in thepresent invention, the formation of the carbon film 20 on the moldingsurface of the metal mold 10, and the aging treatment of the metal mold10 are performed at the same time in the film-forming step S20. Thismakes it possible to make the metal mold 10 desired hardness without theeffect of the aging treatment weakening.

As mentioned above, in the step S1, the surface-treated mold 1 ismanufactured by performing the modeling step S10 and the film-formingstep S20 in this order.

The molding surface of the metal mold 10 produced in the modeling stepS10 is rough owing to the plurality of protrusions 11. However, sincethe dense carbon film 20 is formed on the molding surface of the metalmold 10 in the film-forming step S20, the molding surface of thesurface-treated mold 1 is dense.

Conventionally, rough processing for forming the shape of the metalmold, and finishing processing for smoothing the surface thereof areperformed in this order, and thereby the metal mold is produced. Afterthat, the surface of the metal mold is worked into the bumpy surface bymeans of shot blasting or the like, and the film such as the carbon filmis formed on the bumpy surface.

On the other hand, in the present invention, the metal mold 10 havingthe rough surface is produced in the modeling step S10, and then thedense carbon film 20 is formed on the molding surface of the metal mold10 in the film-forming step S20, thereby manufacturing thesurface-treated mold 1. Therefore, the surface processing such as thefinishing processing and the shot blasting does not need to beperformed.

This makes it possible to reduce the time and the cost required formanufacturing the surface-treated mold 1.

Moreover, in the modeling step S10, the metal powder is melted with alaser, and solidifies, thereby producing the metal mold 10. Therefore,the surface of the metal mold 10 is activated, namely, the newly-formedsurface of the metal mold 10 is exposed.

In particular, in the step S1, the film-forming step S20 is performedwithout performing the surface processing such as the finishingprocessing and the shot blasting after the modeling step S10. This makesit possible to keep the molding surface of the metal mold 10 activatedwithout an oxide film forming on the molding surface of the metal mold10 even when the carbon film 20 is formed on the molding surface of themetal mold 10.

Therefore, in the film-forming step S20, a reaction between the moldingsurface of the metal mold 10 and reactive gas such as acetylene gas ispromoted, thus enabling to form the firm carbon film 20 in a short time.

Not only a metal mold such as the surface-treated mold 1 but also asliding member such as a plunger tip may be used as a casting memberaccording to the present invention.

For example, in the case where a plunger tip is used as a casting memberaccording to the present invention, a film similar to the carbon film 20is preferably formed on the outer circumferential surface (slidingsurface) of the plunger tip.

INDUSTRIAL APPLICABILITY

The present invention is applied to a casting member such as a metalmold, and to a method for manufacturing the casting member.

REFERENCE SIGNS LIST

1: surface-treated mold (casting member)

10: metal mold (base material)

11: protrusion

20: carbon film

1. A casting member used for casting, comprising: a base materialmanufactured by means of selective laser sintering, which has a surfaceincluding a plurality of minute irregularities each having aninverse-slope shape; and a film formed on the surface of the basematerial.
 2. The casting member according to claim 1, wherein the basematerial is a metal mold having a molding surface, and the film isformed on the molding surface of the metal mold.
 3. A method formanufacturing a casting member used for casting, comprising: a modelingstep for producing a base material, by means of selective lasersintering, which has a surface including a plurality of minuteirregularities each having an inverse-slope shape; and a film-formingstep for forming a film on the surface of the base material produced inthe modeling step.
 4. The method according to claim 3, wherein the filmis a carbon film including at least one kind of nanocarbon, and in thefilm-forming step, the carbon film is formed on the surface of the basematerial by heating the base material while supplying a reactive gasused to make the carbon film.
 5. The method according to claim 4,wherein a temperature and a time for heating the base material in thefilm-forming step are set to a temperature and a time for performing anaging treatment for hardening the base material, respectively.